Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/20—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces by extruding
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
  • B22F3/12—Both compacting and sintering
  • B22F3/1208—Containers or coating used therefor

Definitions

• the invention relates to a method for producing powder-metallurgical objects, in particular elongated objects, such as rods, profiles, pipes or the like, in which powder made of metal and / or metal alloys of high hardness, in particular tool steel or high-speed steel powder, is filled into a thin-walled capsule which The capsule is then sealed airtight, heated and isostatically pressed to produce a blank, which is then thermoformed, in particular extruded, to give the end product.
• Such a method is e.g. B. from DE-C-35 30 741 known.
• a powder density of a maximum of 75% of the theoretical density can be achieved with conventional cold isostatic pressing. Due to the hardness of the metal powder used here, a close bond between the capsule material and the adjacent metal powder cannot be achieved with isostatic pressing with the result that the relatively soft capsule material forms folds or "wrinkles" during extrusion. This phenomenon results in surface cracks in the end product, which appear after the capsule material has been removed.
• AT-A-377 718 describes a process for producing products from tool steel powder, the powder being introduced into a capsule, the capsule being airtight, heated and then the capsule filled with powder being extruded, the capsule being airtight to a temperature of Heated from 700 ° C to 1000 ° C, the air access to the capsule is released again and the capsule is subsequently heated to a temperature of 1050 ° C 1200 ° C.
• it is still necessary to anneal the extruded rods for several hours in order to then gradually step them down to a lower temperature and then continue to cool uncontrolled in air.
• This procedure also proves to be relatively complex, although it appears questionable to open the capsule again after heating to a temperature of 700 ° C. to 1000 ° C. in order to then heat it to an even higher temperature. With this procedure there is an increased risk of oxidation, so that the feasibility of this process is doubtful.
• the present invention has for its object to provide a method of the type mentioned, with the defect-free or crack-free objects, in particular elongated objects using powder made of metal and / or metal alloys of high hardness, in particular from tool steel in a simple manner. or high-speed steel powder.
• the cooling time is noticeably longer than the soaking time and the time during which the capsule is increased Temperature is maintained.
• the capsule is preferably cooled to about 3 to 5 hours.
• the capsule can be cooled to ambient temperature by heating the capsule and keeping it at an elevated temperature. This results in an extremely "gentle" cooling, ie a relatively slow cooling rate without a deterrent effect.
• the cold isostatic pressing of the capsule is expediently carried out at a pressure of approximately 4500 to 5500 bar. At these pressures, the metal powder, which has already been made relatively compliant by the thermal pretreatment, is compacted sufficiently to obtain fault-free products during the subsequent hot forming.
• the press blank should be kept at elevated temperature for a longer time, preferably up to 4 to 5 hours.
• the tool steel powder with an average particle size of 125 ⁇ and maximum particle size of approximately 600 ⁇ was filled into a thin-walled capsule made of low-carbon steel with a diameter of 120 mm and a length or height of 600 mm.
• the capsule was then closed and subjected to cold isostatic pressure, namely at a pressure of approximately 5000 bar.
• a powder density of approximately 75% of the theoretical density was achieved.
• the press blank was then heated to the hot forming temperature. Then the blank was extruded. The end product showed unacceptable cracks and had to be evaluated as a committee. The application of a higher pressure during cold isostatic pressing did not lead to a better result.
• the tool steel powder according to Example 1 was also filled into a capsule according to Example 1.
• the capsule was then sealed airtight. Then the capsule was heated to 1150 ° C. until the capsule was continuously at this temperature. The capsule was kept at this temperature for about 1 hour. Then there was a slow cooling, namely oven cooling. The cooling down to ambient temperature stretched over 4 hours.
• the capsule was then cold isostatically pressed and extruded. A cold density of about 80% of the theoretical density was obtained by the cold isostatic pressing. A higher density was not necessary despite the use of tool steel powder, which has a relatively high resistance to deformation not only at a low but also at a high temperature. Despite this property of the metal powder used, the theoretical density was obtained in the end product. Furthermore, the end product showed no defects, ie no cracks.
• the capsule filled with tool steel powder according to Example 1 was cold-isostatically compressed after airtight sealing, to achieve a powder density of about 75% of the theoretical density.
• This green compact was then heated to 1150 ° C. After complete heating, the press blank was held at this temperature for about 1 hour. Then slow cooling followed. The cooling time in the oven was about 3 hours. After this treatment, the powder density was approximately 80% of the theoretical density. The extrusion of the pressed blank then took place. The final product had theoretical density and showed no defects, especially cracks.
• the carbon content of the metal powder is not particularly critical when using the methods described above, i. H. Metal powder with a high carbon content can also be processed into perfect end products using powder metallurgy.

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Powder Metallurgy (AREA)
• Metal Rolling (AREA)

Applications Claiming Priority (4)

Publications (2)

Family

ID=26660106

Family Applications (1)

Country Status (4)

Cited By (1)

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• 1989
  • 1989-02-01 EP EP89101731A patent/EP0327064A3/fr not_active Ceased
  • 1989-02-04 KR KR1019890001356A patent/KR890012729A/ko not_active Withdrawn
  • 1989-02-06 US US07/308,048 patent/US4923671A/en not_active Expired - Fee Related
  • 1989-02-06 JP JP1025970A patent/JPH01287205A/ja active Pending

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